Tilting pad bearing device

ABSTRACT

An object is to provide a tilting-pad bearing device whereby it is possible to levitate a rotation shaft with a low supply-oil pressure. A tilting-pad bearing device includes a plurality of bearing pads disposed around a rotation shaft so as to support the rotation shaft rotatably, a support member interposed between the plurality of bearing pads and a bearing housing supporting the plurality of bearing pads, the support member supporting each of the plurality of bearing pads pivotably, and an oil-supply mechanism configured to supply a lubricant oil to at least one oil groove formed on a bearing surface of at least one of the plurality of bearing pads. The at least one oil groove is disposed inside and outside a contact area of the bearing surface which is in contact with an outer circumferential surface of the rotation shaft when the rotation shaft is stopped.

TECHNICAL FIELD

The present invention relates to a tilting-pad bearing device whichsupports a rotation shaft of a large-sized rotary machine with aplurality of pivotable bearing pads, such as a slide bearing for a steamturbine.

BACKGROUND

In a large-sized rotary machine such as a turbine and a generator, atilting-pad bearing device is used to support a rotation shaft stably. Atilting-pad bearing device is a kind of slide bearings, and includes aplurality of pivotable bearing pads (tilting pads) disposed around therotation shaft inside a bearing housing. The bearing pads are pivotablysupported by pivots disposed inside the bearing housing. When therotation shaft rotates, lubricant oil is introduced into a gap betweenthe outer circumferential surface of the rotation shaft and the bearingsurface of the bearing pads to form an oil film of a wedge shape betweenthe above surfaces, and thereby the tilting-pad bearing device supportsthe rotation shaft. For instance, Patent Document 1 discloses such atilting-pad bearing device.

In such a tilting-pad bearing device, it is necessary to eliminatecontact between the outer circumferential surface of the rotation shaftand the bearing surface of the tilting pad at the beginning of rotationor at low-speed rotation when an adequate load capability cannot beobtained from the wedge effect of the oil film, so as to prevent gallingof the bearing surface. In this regard, a mechanism called a jacking oilpump (JOP mechanism) may be employed. For instance, in the JOP mechanismdescribed in Patent Document 2, an oil-supply inlet is disposed on thebearing surface of the tilting pad, and high-pressure lubricant oil issupplied to the oil-supply inlet from a pump via an oil-supply channelto form an oil film on the bearing surface so that the rotation shaft islevitated by the oil film. Normally, oil grooves are formed on thebearing surface to distribute the lubricant oil over a broad region.

CITATION LIST Patent Literature

Patent Document 1: JPS59-212520A

Patent Document 2: JPH02-146961U

SUMMARY Problems to be Solved

The tilting-pad bearing device is configured such that the bearing padsare supported by pivots contacting the outer circumferential surfaces ofthe bearing pads so as to be pivotable. Thus, the bearing pads slightlydeform due to the self-weight of the bearing pads or a load or the likeapplied to the bearing pads via the rotation shaft. Thus, when therotation shaft stops, the bearing pads contact the rotation shaft in acontact area having a shape which depends on the deformation of thebearing pads. In a case where the bearing pads are point-supported bythe pivots, for instance, the contact area between the bearing pads andthe rotation shaft has a substantially ellipse shape.

Here, as a result of intensive researches of the present inventors, itwas found that the levitation characteristic of the rotation shaftachieved by the JOP mechanism is affected by a relationship in therelative arrangement between: the contact area of each bearing pad andthe rotation shaft at the time when the rotation shaft is stopped; andthe oil grooves for introducing lubricant oil disposed on the bearingsurface of the bearing pad. In other words, depending on therelationship in the relative arrangement between the contact area andthe oil grooves, the supply hydraulic pressure to the JOP mechanismrequired to levitate the rotation shaft varies.

However, Patent Documents 1 and 2 do not disclose a relationship in therelative arrangement between the contact area and the oil grooves whichenables levitation of the rotation shaft with the JOP mechanism even ifthe pressure of the supply oil to the JOP mechanism is low.

An object of at least some embodiments of one aspect of the presentinvention is to provide a tilting-pad bearing device whereby it ispossible to levitate the rotation shaft with a low supply hydraulicpressure.

Further, an object of at least some embodiments of another aspect of thepresent invention is to provide a tilting-pad bearing device whereby itis possible to prevent contact between the rotation shaft and thebearing pad.

Solution to the Problems

A tilting-pad bearing device according to some embodiments of thepresent invention includes: a plurality of bearing pads disposed arounda rotation shaft so as to support the rotation shaft rotatably; asupport member interposed between the plurality of bearing pads and abearing housing supporting the plurality of bearing pads, the supportmember supporting each of the plurality of bearing pads pivotably; andan oil-supply mechanism configured to supply a lubricant oil to at leastone oil groove formed on a bearing surface of at least one of theplurality of bearing pads. The at least one oil groove is disposedinside and outside a contact area of the bearing surface which is incontact with an outer circumferential surface of the rotation shaft whenthe rotation shaft is stopped.

With the above tilting-pad bearing device, the oil grooves are disposedinside and outside the contact area of the bearing surface contactingthe outer circumferential surface of the rotation shaft, and thelubricant oil is supplied to the oil grooves from the oil-supplymechanism. Thus, it is possible to distribute the lubricant oil to bothinside and outside the contact area when the lubricant oil is suppliedfrom the oil-supply mechanism via the oil grooves at the beginning ofthe rotation of the rotation shaft or at low-speed rotation of therotation shaft. As a result, even if the supply hydraulic pressure tothe oil-supply mechanism is relatively low, it is possible to levitatethe rotation shaft effectively.

Here, the contact area is determined from the diameter of the rotationshaft (the curvature radius of the outer circumferential surface of therotation shaft), the curvature radius of the bearing surface of thebearing pad, the material of the bearing pad, and the load or the likeapplied to the tilting-pad bearing device via the rotation shaft. Theshape and position of the contact area may be obtained on a trial basis,or may be estimated by simulation. For instance, a sheet of carbonlesscopy paper may be interposed between the rotation shaft and the bearingpad, and a colored area of the sheet of carbonless copy paper may bedetermined as the contact area. Alternatively, the contact area may beestimated from the contact stress calculated by using the Hertz theory,or may be estimated using the FEM analysis.

Further, a tilting-pad bearing device according to at least someembodiments of another aspect of the present invention includes: aplurality of bearing pads disposed around a rotation shaft so as tosupport the rotation shaft rotatably; a support member interposedbetween the plurality of bearing pads and a bearing housing supportingthe plurality of bearing pads, the support member supporting each of theplurality of bearing pads pivotably; and an oil-supply mechanismconfigured to supply a lubricant oil to at least one oil groove formedon a bearing surface of at least one of the plurality of bearing pads.

The support member is disposed so as to be offset from a middle positionof the at least one bearing pad in a rotational direction of therotation shaft, toward an upstream side or a downstream side in therotational direction of the rotation shaft. A weighted mean position ofthe at least one oil groove representing a mean position of a respectivecenter position of the at least one oil groove in a circumferentialdirection of the rotation shaft weighted by a respective opening area ofthe at least one oil groove is offset from an arrangement position ofthe support member, in an offset direction of the support member basedon the middle position.

With the above tilting-pad bearing device, the weighted mean position ofthe oil groove representing the mean position of the center positionsx_(i) of the respective oil grooves weighted by the opening areas S_(i)of the oil grooves is offset in an offset direction of the supportmember from the arrangement position of the support member. Thus, evenif the support member is offset, it is possible to restrict the gapbetween the outer circumferential surface of the rotation shaft and anend of the bearing pad at the offset side from being smaller than thegap between the outer circumferential surface of the rotation shaft andan end of the bearing pad at the opposite side of the offset direction.In this way, it is possible to restrict inclination of the rotationshaft, and to prevent the rotation shaft from contacting the bearingpad, at the beginning of rotation of the rotation shaft or at low-speedrotation of the rotation shaft.

In one embodiment, the at least one oil groove extends continuously frominside to outside of the contact area.

As described above, providing the at least one oil groove extendingcontinuously form inside to outside of the contact area makes itpossible to reduce the number of the oil grooves while maintaining thelevitation performance of the rotation shaft achieved by the oilgrooves.

In another embodiment, the at least one oil groove includes an inner oilgroove disposed inside the contact area and an outer oil groove disposedoutside the contact area separately from the inner oil groove.

As described above, providing the inner oil groove disposed inside thecontact area and the outer oil groove disposed outside the contact areamakes it possible to improve the flexibility of the position and shapeof each oil groove while maintaining the levitation performance of therotation shaft achieved by the oil grooves.

In some embodiments, each of the at least one oil groove is disposedalong a constant-pressure line passing through positions having samepressure of an oil film formed between the bearing surface and the outercircumferential surface of the rotation shaft when the rotation shaft isrotating.

Each oil groove is formed by a single communicating space. Thus, thepressure is the same at any position in each of the oil grooves.Accordingly, if the oil grooves were formed over differentconstant-pressure lines, the pressures in the respective oil groovescould be averaged upon rotation of the rotation shaft, hindering thefunction as a hydrodynamic bearing. In view of this, as in the aboveembodiment, each oil groove is disposed along a constant-pressure line,which makes it possible to maintain the pressures inside the oil groovesat the respective constant-pressure line positions, and to maintain agood function as a hydrodynamic bearing.

In one embodiment, the at least one oil groove comprises at least onefirst oil groove disposed along a first constant-pressure line passingthrough positions where the pressure of the oil film is a firstpressure, and at least one second oil groove disposed along a secondconstant-pressure line passing through positions where the pressure ofthe oil film is a second pressure which is different from the firstpressure. The oil-supply mechanism includes a first oil-supply channelcommunicating with the at least one first oil groove, and a secondoil-supply channel communicating with the at least one second oilgroove. The first oil-supply channel and the second oil-supply channelare separate systems capable of maintaining pressures different fromeach other at least when the rotation shaft is rotating.

According to the above embodiment, the first oil-supply passagecommunicating with the first oil groove and the second oil-supplypassage communicating with the second oil groove are provided asseparate systems so as to be capable of maintaining pressures differentfrom each other at least when the rotation shaft rotates. In this way,it is possible to prevent the pressures of the first oil groove and thesecond oil groove disposed along different constant-pressure lines (thefirst and second constant-pressure lines) from being averaged when therotation shaft is rotating at a rated rotation speed, and to maintain agood function as a hydrodynamic bearing.

In one embodiment, the at least one first oil groove disposed along thefirst constant-pressure line comprises a plurality of first oil groovescommunicating with each other via the first oil-supply channel.

As described above, adopting a configuration in which the oil-supplychannels communicate with each other for the plurality of the first oilgrooves disposed along the same constant-pressure line makes it possibleto simplify the configuration of the oil-supply mechanism such as theoil-supply channels and the valve.

In some embodiments, the tilting-pad bearing device further includes: afirst valve for adjusting an amount of the lubricant oil supplied to theat least one first oil groove, the first valve being disposed in thefirst oil channel; and a second valve for adjusting an amount of thelubricant oil supplied to the at least one second oil groove, the secondvalve being disposed in the second oil channel.

When the JOP mechanism is operated such as at the beginning of rotationof the rotation shaft or at low-speed rotation of the rotation shaft, itis possible to adjust the amount of lubricant oil supplied to each oilgroove by adjusting the opening degree of each valve. On the other hand,when the lubricant oil is not supplied to the bearing surface such aswhen the rotation shaft is rotating at a rated rotation speed, it ispossible to prevent leakage of the lubricant oil from the oil channelsby shutting off the oil channels with the respective valves. As aresult, it is possible to maintain the oil-film pressure of the bearingsurface suitably.

In some embodiments, the support member is disposed so as to be offsetfrom a middle position of the at least one bearing pad in a rotationaldirection of the rotation shaft, toward an upstream side or a downstreamside in the rotational direction of the rotation shaft. A weighted meanposition of the at least one oil groove representing a mean position ofa respective center position of the at least one oil groove in acircumferential direction of the rotation shaft weighted by a respectiveopening area of the at least one oil groove is offset from anarrangement position of the support member, in an offset direction ofthe support member based on the middle position.

A moment about the support point of the bearing pad supported by thesupport member is applied to the bearing pad of the tilting-pad bearingdevice, in accordance with the distribution of the oil-film pressureformed between the rotation shaft and the bearing pad during operationof the JOP mechanism (i.e., while the lubricant oil is supplied) at thebeginning of rotation of the rotation shaft or at low-speed rotation ofthe rotation shaft. This moment is obtained by adding up local momentsof all positions on the bearing surface, each local moment being aproduct of the oil-film pressure at a certain position on the bearingsurface and a distance between the certain position and the supportpoint. The local moments have opposite signs at either side of thesupport point of the bearing pad supported by the support member. Thus,the direction of the net moment corresponding to the distribution of theoil-film pressure formed between the rotation shaft and the bearing padis determined depending on the magnitude relationship of the absolutevalue of the moment at either side of the support point of the bearingpad supported by the support member. Here, the contribution of each oilgroove to the local moment is represented by a product x_(i)S_(i) of thecenter position x_(i) (i=1, 2) of each oil groove and the opening areaS_(i) (i=1, 2) of the oil groove affecting the magnitude of the oil-filmpressure formed by the oil groove. Thus, the direction of the net momentcorresponding to the distribution of the oil-film pressure is basicallydetermined by the sum Σx_(i)S_(i) (i=1, 2) of contribution to the localmoment in each oil groove. In other words, the direction of the netmoment corresponding to the distribution of the oil-film pressure isdetermined depending on the arrangement relationship between theposition of the support member and a value obtained by dividing the sumΣx_(i)S_(i) by the sum ΣS_(i) of the opening areas of all oil grooves.The value here is the weighted mean position x_(A) of the oil grooverepresenting the mean position of the center positions x_(i) of therespective oil grooves weighted by the opening areas S_(i) of the oilgrooves.

With the above tilting-pad bearing device, the weighted mean position ofthe oil grooves representing the mean position of the center positionsof the respective oil grooves weighted by the opening areas of the oilgrooves is offset in an offset direction of the support member from thearrangement position of the support member. Thus, even if the supportmember is offset, it is possible to balance the moment applied to theupstream side and the downstream side of the rotation shaft in therotational direction with reference to the support member. In this way,it is possible to restrict inclination of the rotation shaft, and toprevent the rotation shaft from contacting the bearing pad, at thebeginning of rotation of the rotation shaft or at low-speed rotation ofthe rotation shaft.

In one embodiment, the support member is disposed on the downstreamside, in the rotational direction of the rotation shaft, of the middleposition of the bearing pad in the circumferential direction of therotation shaft. The weighted mean position of the at least one oilgroove is offset toward the downstream side in the rotational directionof the rotation shaft from the arrangement position of the supportmember.

In some embodiments, a plurality of oil-supply inlets which is suppliedwith the lubricant oil from the oil-supply mechanism is disposed on thebearing surface so as to be arranged in a line in an axial direction ofthe rotation shaft, each of the plurality of oil-supply inletscommunicating with corresponding one of the at least one oil grooveformed independently from one another.

In this way, even if there is a partial contact in the axial directionof the rotation shaft, it is possible to remedy the partial contact byadjusting the oil-film pressure of each oil groove by adjusting theamount of lubricant oil supplied to each oil groove.

In some embodiments, the at least one oil groove is disposed within aregion in which an oil-film pressure due to a wedge-shaped oil filmformed on the bearing surface is uniform when the rotation shaft isrotating.

If one continuous oil groove is formed over regions having differentoil-film pressures formed between the rotation shaft and the bearingpad, the oil-film pressure of the oil groove decreases following thelower one of the oil-film pressures. In contrast, if one oil groove isformed in a region having the same oil-film pressure like the aboveembodiment, it is possible to prevent such a decrease in the oil-filmpressure.

In some embodiments, when the rotation shaft is rotating, aconstant-pressure region in which an oil-film pressure due to awedge-shaped oil film formed on the bearing surface is uniform is formedsuch that a maximum oil-film pressure region is at a center and a regionhaving a gradually decreasing oil-film pressure spreads outwardly fromthe maximum oil-film pressure region in a concentric fashion. The atleast one oil groove is disposed along one constant-pressure line.

As described above, providing the oil groove along the constant-pressureline in the distribution of the oil-film pressure formed during rotationof the rotation shaft, which is a distribution in which a region with agradually decreasing oil-film pressure is spreading in a concentricfashion outwardly from the maximum oil-film pressure region at thecenter, makes it possible to maintain a good function as a hydrodynamicbearing.

In some embodiments, a gap between the rotation shaft and an upstreamend of the bearing pad in the rotational direction is distributed in arange equivalent to a gap between the rotation shaft and a downstreamend of the bearing pad in the rotational direction, due to an oil-filmpressure generated between the outer circumferential surface of therotation shaft and the bearing surface when the rotation shaft isrotating.

Advantageous Effects

According to some embodiments of the present invention, the oil groovesare disposed inside and outside the contact area of the bearing surfacecontacting the outer circumferential surface of the rotation shaft, andthe lubricant oil is supplied to the oil grooves from the oil-supplymechanism. Thus, it is possible to distribute the lubricant oil to bothinside and outside the contact area when the lubricant oil is suppliedfrom the oil-supply mechanism via the oil grooves at the beginning ofthe rotation of the rotation shaft or at low-speed rotation of therotation shaft. As a result, even if the supply hydraulic pressure tothe oil-supply mechanism is relatively low, it is possible to levitatethe rotation shaft effectively.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an overall configuration diagram of a bearing device accordingto the first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a bearing pad according to the firstembodiment.

FIG. 3 is a developed view of a bearing surface of a bearing padaccording to the first embodiment.

FIG. 4 is a developed view of a bearing surface of a bearing pad of acomparative example, where oil grooves are disposed only inside acontact area.

FIG. 5 is a developed view of a bearing surface of a bearing pad ofanother comparative example, where oil grooves are disposed only outsidea contact area.

FIGS. 6A to 6C are each a graph of a relationship between a contact areaand an oil-film pressure.

FIG. 7 is a configuration diagram of an example of an oil-supplymechanism of the bearing device according to the first embodiment.

FIG. 8 is a developed view of a bearing surface according to the secondembodiment of the present invention.

FIG. 9 is a configuration diagram of an example of an oil-supplymechanism of the bearing device according to the second embodiment ofthe present invention.

FIG. 10 is a developed view of a bearing surface according to the thirdembodiment of the present invention.

FIG. 11 is a cross-sectional view of a bearing device according to thefourth embodiment of the present invention.

FIG. 12 is a developed view of a bearing surface of the bearing padaccording to the fourth embodiment of the present invention.

FIG. 13 is a diagram for describing a weighted mean position of an oilgroove.

FIG. 14 is a developed view of a bearing surface of a bearing padaccording to the fifth embodiment of the present invention.

FIG. 15 is a diagram of pressure distribution of an oil film accordingto the fifth embodiment of the present invention.

FIG. 16 is a developed view of a bearing surface of a bearing padaccording to the sixth embodiment of the present invention.

FIG. 17A is a diagram of pressure distribution of an oil film in the oilgroove according to the fourth embodiment, and FIG. 17B is a diagram ofpressure distribution of an oil film in the oil groove according to thesixth embodiment.

FIG. 18 is a developed view of a bearing surface of a bearing padaccording to a modified example of the sixth embodiment.

FIG. 19 is a cross-sectional view of a bearing device illustrating anoil-supply mechanism according to a modified example of the sixthembodiment.

DETAILED DESCRIPTION

Embodiments of the present invention will now be described in detailwith reference to the accompanying drawings. It is intended, however,that unless particularly specified, dimensions, materials, shapes,relative positions and the like of components described in theembodiments shall be interpreted as illustrative only and not limitativeof the scope of the present invention.

First Embodiment

With reference to FIG. 1, the overall schematic configuration of atilting-pad bearing device 10 according to the first embodiment of thepresent invention will be described. FIG. 1 is an overall configurationdiagram of a tilting-pad bearing device according to the firstembodiment of the present invention.

In some embodiments, a bearing housing 12 illustrated in FIG. 1 is abearing housing of a halved type, which includes semicircle-shapedhousing segments 12 a and 12 b. The housing segments 12 a and 12 b arejoined to each other by coupling units such as bolts while the couplingsurfaces of the housing segments 12 a and 12 b are in contact. Aplurality of (four in FIG. 1) bearing pads 14 is disposed along theinner circumferential surface of the bearing housing 12, and the innercircumferential surface of each bearing pad 14 forms a bearing surface14 a. Inside the bearing surfaces 14 a, a rotation shaft 15 (see FIG. 2)of a large-sized rotary machine such as a turbine and a generator isdisposed. An oil-supply inlet 34 is disposed, and an oil groove 36communicating to the oil-supply inlet 34 is engraved, on the bearingsurface 14 a of at least one of the bearing pads 14 among the pluralityof bearing pads 14, 14, and so on. The bearing pad 14 with theoil-supply inlet 34 and the oil groove 36 may be at least a bearing pad14 disposed at the lower part in the circumferential direction of therotation shaft 15 of the plurality of bearing pads 14, 14, and so ondisposed around the rotation shaft 15. Specifically, the supply-oilinlet 34 and the oil groove 36 may be formed on the bearing pad 14disposed at a position that supports the self-weight of the rotationshaft 15 when the rotation shaft 15 is stopped. It will be understoodthat the oil-supply inlet 34 and the oil groove 36 may be formed on thebearing pad 14 disposed at the upper part in the circumferentialdirection of the rotation shaft 15.

Now, the configuration of an oil-supply mechanism 16 that supplieslubricant oil to the oil-supply inlet 34 will be described. A pump 18 isdriven by a motor 20 so as to supply high-pressure lubricant oil “o” toan oil-supply line 22 from an oil tank (not illustrated). A relief valve24 is disposed in an oil channel 22, so that a part of the lubricant oilflowing through the oil channel 22 is emitted into a tank 26 to reducethe pressure of the lubricant oil “o” to a tolerance or less, when thepressure of the lubricant oil “o” exceeds the tolerance. The oil-supplyline 22 branches into branch channels 28 a and 28 b at the downstreamside. The branch channels 28 a and 28 b respectively include valves(flow-rate adjustment valves) 30 a and 30 b. The branch channels 28 aand 28 b communicate with the oil-supply inlet 34 formed on each bearingpad 14 via oil-supply holes 32 a and 32 b formed through the housingsegments 12 b and the bearing pads 14.

Next, with reference to FIGS. 2 and 3, the specific configuration ofeach part of the tilting-pad bearing device 10 will be described. FIG. 2is a cross-sectional view of a bearing pad according to the firstembodiment of the present invention. FIG. 3 is a developed view of abearing surface of a bearing pad according to the first embodiment ofthe present invention. Specifically, FIG. 3 is a planar developed viewof a bearing pad 14 having a curvature.

In the following embodiment, described as an example is a tilting-padbearing device 10 having a configuration in which the bearing pads 14are point-supported by pivots 38.

In FIG. 2, G₁ is a straight line that passes through the center of therotation shaft 15 and a support point of one of the pivots 38. The arrow“r” in FIG. 2 is the rotational direction of the rotation shaft 15. InFIG. 3, G₂ is a straight line that passes through a support point of thebearing pad 14 supported by the pivot 38 and that is parallel to theaxis of the rotation shaft 15. The arrow “a” represents the axialdirection of the rotation shaft 15.

In some embodiments, the bearing pad 14 illustrated in FIGS. 2 and 3 ispoint-supported so as to be pivotable by the pivot 38 disposed on theinner circumferential surface of the housing segment 12 b. While thepivot 38 is normally disposed in the vicinity of the center of thebearing pad 14, the pivot 38 may be disposed offset toward the upstreamside or the downstream side with respect to the rotational directionfrom the middle position of the bearing pad 14 in the rotationaldirection of the rotation shaft 15. In FIG. 2, the leading edge 14 b ofthe bearing pad 14 in the rotational direction is disposed at theupstream side, while the trailing edge 14 c of the bearing pad 14 in therotational direction is disposed at the downstream side, with respect tothe rotational direction of the rotation shaft 15.

In one embodiment, in FIGS. 2 and 3, the straight line G₂ passingthrough the pivot 38 is disposed offset toward the downstream side inthe rotational direction of the rotation shaft 15, from the middleposition C (see FIG. 13) of the bearing pad 14 in the rotationaldirection of the rotation shaft 15. As described above, in a case wherethe tilting-pad bearing device 10 functions as a hydrodynamic bearingsuch as when the rotation shaft 15 is rotating at a rated rotationspeed, with the pivot 38 being disposed at the downstream side in therotational direction of the rotation shaft 15 with respect to the middleposition of the bearing pad 14 in the circumferential direction of therotation shaft 15, a gap increases between the bearing surface 14 a ofthe leading edge 14 b of the bearing pad 14 and the outercircumferential surface of the rotation shaft 15. As a result, theamount of lubricant oil introduced onto the bearing surface 14 aincreases, which makes it possible to improve lubricating performancebetween the bearing pad 14 and the rotation shaft 15.

In some embodiments, the bearing surface 14 a of the bearing pad 14includes four oil-supply inlets 40 (40 a, 40 b), 44 (44 a, 44 b), andoil grooves 42 (42 a, 42 b), 46 (46 a, 46 b) respectively communicatingwith the oil-supply inlets 40, 44.

In the tilting-pad bearing device 10 having the above configuration, thebearing pad 14 is supported by the pivot 38 contacting the outercircumferential surface of the bearing pad 14 so that the bearing pad 14is pivotable. Thus, the bearing pad 14 slightly deforms due to theself-weight of the bearing pad 14 or the load or the like applied to thebearing pad 14 via the rotation shaft 15. Thus, when the rotation shaft15 is stopped, the bearing pad 14 and the rotation shaft 15 contact eachother in a contact area S that has a shape depending on the deformationof the bearing pad 14. For instance, in a case where the bearing pad 14is point-supported by the pivot 38 as illustrated in FIG. 2, the contactarea S between the bearing pad 14 and the rotation shaft 15 has asubstantially ellipse shape as illustrated in FIG. 3.

In some embodiments, oil grooves 42, 46 are disposed inside and outsidethe contact area S. The contact area S is determined from the diameterof the rotation shaft (the curvature radius of the outer circumferentialsurface of the rotation shaft), the curvature radius of the bearingsurface 14 a of the bearing pad 14, the material of the bearing pad 14,and the load or the like applied to the tilting-pad bearing device 10via the rotation shaft 15. The shape and position of the contact area Smay be obtained on a trial basis, or may be estimated by simulation. Forinstance, a sheet of carbonless copy paper may be interposed between therotation shaft 15 and the bearing pad 14, and a colored area of thesheet of carbonless copy paper may be determined as the contact area S.Alternatively, the contact area S may be estimated from the contactstress calculated by using the Hertz theory, or the contact area S maybe estimated using the FEM analysis.

Now, with reference to FIG. 6, described below is the characteristics ofthe oil-film pressure compared between: the bearing pad 14 according tothe first embodiment illustrated in FIGS. 2 and 3; and the bearing pads14′, 14″ according to the comparison example illustrated in FIGS. 4 and5. FIG. 4 is a developed view of a bearing surface of a bearing pad of acomparative example. FIG. 5 is a developed view of a bearing surface ofa bearing pad of another comparative example, where oil grooves aredisposed only outside the contact area. FIGS. 6A to 6C are each a graphof a relationship between a contact area and an oil-film pressure. FIG.6A is a graph of the characteristics of an oil-film pressure of thebearing pad 14 corresponding to the first embodiment (FIG. 3). FIG. 6Bis a graph of the characteristics of an oil-film pressure of the bearingpad 14′ corresponding to a comparative example (FIG. 4). FIG. 6B is agraph of the characteristics of an oil-film pressure of the bearing pad14′ corresponding to another comparative example (FIG. 5).

For the bearing pad 14′ illustrated in FIG. 4, there is no oil grooveoutside the contact area S, and the oil grooves 42′ (42 a′, 42 b′), 46′(46 a′, 46 b′) are disposed only inside the contact area S. In contrast,for the bearing pad 14″ illustrated in FIG. 5, there is no oil grooveoutside the contact area S, and the oil grooves 42″ (42 a″, 42 b″), 46″(46 a″, 46 b″) are disposed only inside the contact area S.

As illustrated in FIGS. 4 and 6B, in a case where the oil grooves 42′,46′ for introducing the lubricant oil are formed inside the contact areaS, the gap between the bearing pad 14′ and the rotation shaft 15increases rapidly at a boundary from inside to outside the contact areaS. Thus, the oil-film pressure due to the lubricant oil supplied to thegap via the oil grooves 42 a′, 42 b′, 46 a′, 46 b′ in the contact area Sdecreases considerably outside the contact area S due to the rapidincrease in the volume of the gap, although the oil-film pressure ismaintained to be high inside the contact area S. Thus, it is difficultto distribute the lubricant oil so as to form a substantially-uniformoil-film pressure over the entire bearing surface of the bearing pad14′. The oil-film pressure may become insufficient especially outsidethe contact area S.

As illustrated in FIGS. 5 and 6C, in a case where the oil grooves 42″,46″ are formed outside the contact area S, the gap between the bearingpad 14″ and the rotation shaft 15 rapidly decreases at a boundary fromoutside to inside the contact area S. Thus, the lubricant oil may not besupplied sufficiently into contact area S, and the oil-film pressure maybecome insufficient inside the contact area S.

As described above, in the case of the bearing pads 14′, 14″ in thecomparison examples, there is a risk that lubricant oil is notdistributed sufficiently over the bearing surfaces 14 a′, 14 a″ of thebearing pads 14′, 14″, and the rotation shaft 15 does not levitatesmoothly when the JOP mechanism is started to rotate the rotation shaft15.

In contrast, in the present embodiment, as illustrated in FIGS. 3 and6A, the oil grooves 42, 46 are disposed inside and outside the contactarea S, which makes it possible to distribute the lubricant oil to bothinside and outside the contact area S when the lubricant oil is suppliedfrom the oil-supply mechanism 16 via the oil grooves 42, 46 at thebeginning of the rotation of the rotation shaft 15 or at low-speedrotation of the rotation shaft 15. As a result, even when the supplyhydraulic pressure to the oil-supply mechanism 16 is relatively low, itis possible to levitate the rotation shaft 15 effectively.

Further, in one embodiment, the at least one oil groove 42, 46 mayextend continuously from inside to outside the contact area S. That is,each oil groove 42, 46 may extend so as to cross the boundary of thecontact area S. Providing the at least one oil groove 42, 46 extendingcontinuously form inside to outside of the contact area S as describedabove makes it possible to reduce the number of the oil grooves 42, 46while maintaining the levitation performance of the rotation shaft 15achieved by the oil grooves 42, 46. In the example illustrated in FIG.3, all of the oil grooves 42, 46 are disposed so as to extendcontinuously from inside to outside the contact area S.

Further, in another embodiment that is not illustrated in the drawings,the at least one oil groove may include an inner oil groove disposedinside the contact area S and an outer oil groove disposed outside thecontact area S separately from the inner oil groove. Providing the inneroil groove disposed inside the contact area S and the outer oil groovedisposed outside the contact area S makes it possible to improve theflexibility of the installation position and shape of each oil groovewhile maintaining the levitation performance of the rotation shaft 15achieved by the oil grooves.

Further, in some embodiments, each of the at least one oil groove 42, 44may be disposed along a constant-pressure line that passes throughpositions having the same pressure of an oil film formed between thebearing surface 14 a and the outer circumferential surface of therotation shaft 15 when the rotation shaft 15 rotates.

When the rotation shaft 15 rotates at a high speed, supply of thelubricant oil to the oil-supply inlets 40, 44 disposed on the bearingsurface 14 a of the bearing pad 14 is stopped. At this time, thelubricant oil forms an oil-film pressure while rotating along with therotation shaft 15, and the distribution of the oil-film pressure (seeFIG. 3) is formed by the oil-film pressure. In FIG. 3, the lines p1 top6 are constant-pressure lines of an oil film having a wedge shapeformed from rotation of the shaft, where an interior region of theconstant-pressure line p1 disposed at the innermost has the maximumoil-film pressure, the oil-film pressure decreasing sequentially towardthe outside. As illustrated in the drawing, the distribution has anellipse shape centered at the maximum oil-film pressure region (theinner region of p1) and constant-pressure regions spread in a concentricfashion. Here, a constant-pressure line is a line passing throughpositions having the same pressure of the oil film formed between thebearing surface 14 a and the outer circumferential surface of therotation shaft 15 when the rotation shaft 15 rotates.

In one embodiment, the oil-supply inlets 40 (40 a, 40 b) illustrated inFIG. 3 are all disposed on the constant-pressure line p4. Further, theoil grooves 42 (42 a, 42 b) communicating with the oil-supply inlets 40are all disposed along the constant-pressure line p4. Similarly, the oilgrooves 46 (46 a, 46 b) communicating with the oil-supply inlets 44 (44a, 44 b) are disposed along the constant pressure line p5. The oilgrooves 42 are independently provided from the oil grooves 46.

Each oil groove 42, 44 is formed by a single communicating space. Thus,the pressure is the same at any position in each of the oil grooves 42,44. Accordingly, if the oil grooves 42, 44 were formed over differentconstant-pressure lines, the pressures in the respective oil grooves 42,44 could be averaged upon rotation of the rotation shaft 15, hinderingthe function as a hydrodynamic bearing. In view of this, as in the aboveembodiment, the oil grooves 42, 44 are respectively disposed along theconstant-pressure line p4, p5, which makes it possible to maintain thepressures inside the oil grooves 42, 44 at the respectiveconstant-pressure line positions, and to maintain a good function as ahydrodynamic bearing.

Further, in one embodiment, as illustrated in FIG. 7, oil-supplychannels 52, 54 which supply lubricant oil to the oil grooves 42 and theoil grooves 44 are provided as a separate system so as to be capable ofmaintaining different pressures from one another at least when therotation shaft 15 rotates.

The oil-supply mechanism 16 illustrated in FIG. 7 includes the firstoil-supply inlet 40, the first oil groove 42, the second oil-supplyinlet 44, the second oil groove 46, the first oil-supply channel 52, thesecond oil-supply channel 54, the first valve 53, the second valve 55,and the pump 50.

The first oil groove 42 and the second oil groove 46 are disposed alongconstant-pressure lines representing different oil-film pressures. Thefirst oil-supply channel 52 and the second oil-supply channel 54 areprovided as separate systems so as to be capable of maintainingdifferent pressures from one another at least when the rotation shaft 15rotates. The first oil-supply channel 52 and the second oil-supplychannel 54 are connected to the pump 50 so as to be supplied with thelubricant oil by the pump 50. The first valve 53 is disposed between thefirst oil-supply channel 52 and the pump 50, and the second valve 55 isdisposed between the second oil-supply channel 54 and the pump 50, sothat the amount of lubricant oil supplied to the first oil-supplychannel 52 and the second oil-supply channel 54 is adjustable.

At the beginning of rotation of the rotation shaft 15 or at low-speedrotation of the rotation shaft 15, the first valve 53 and the secondvalve 55 are each opened, and the pump 50 is operated to supplylubricant oil to the first oil groove 42 and the second oil groove 46via the first oil-supply channel 52 and the second oil-supply channel54. The amount of lubricant oil supplied to each oil groove 42, 46 maybe adjusted by the opening degree of each valve 53, 55. On the otherhand, when the rotation shaft 15 is rotating at a rated rotation speed,the first valve 53 and the second valve 55 are closed, and the pump 50is stopped to shut off supply of lubricant oil to the first oil groove42 and the second oil groove 46 via the first oil-supply channel 52 andthe second oil-supply channel 54. At this time, since the first oilgroove 42 and the second oil groove 46 are not in communication, thepressures of the oil grooves 42, 46 are maintained independently fromeach other.

As described above, the first oil-supply channel 40 communicating withthe first oil groove 42 and the second oil-supply channel 44communicating with the second oil groove 46 are provided as separatesystems so as to be capable of maintaining pressures different from eachother at least when the rotation shaft 15 rotates. In this way, it ispossible to prevent the pressures of the first oil groove 42 and thesecond oil groove 46 disposed along different constant-pressure lines(the first and second constant-pressure lines) from being averaged whenthe rotation shaft 15 rotates at a rated rotation speed, and to maintaina good function as a hydrodynamic bearing.

Second Embodiment

Next, the second embodiment of the present invention will be describedwith reference to FIGS. 8 and 9. FIG. 8 is a developed view of a bearingsurface of a bearing pad according to the second embodiment of thepresent invention. FIG. 9 is a configuration diagram of an example of anoil-supply mechanism of the bearing device according to the secondembodiment of the present invention.

The oil-supply mechanism 16 according to the present embodiment includesthe first oil-supply inlets 60 (60 a, 60), 64 (64 as, 64 b), the firstoil grooves 62 (62 a, 62 b), 66 (66 a, 66 b), the first oil-supplychannels 72, 74, and the first valve 76 and the pump 70.

A plurality of the first oil grooves 62, 66 is disposed along aconstant-pressure line representing the same oil-film pressure. Further,the oil grooves 62, 66 are configured to communicate with each other viathe first oil-supply channels 72, 74. For instance, the first oil-supplychannels 72, 74 merge at the base side, and the first valve 76 isdisposed between the pump 70 and the merged first oil-supply channels72, 74. The first valve 76 is configured to adjust the amount oflubricant oil supplied to the first oil-supply channels 72, 74.

At the beginning of rotation of the rotation shaft 15 or at low-speedrotation of the rotation shaft 15, the first valve 76 is opened, and thepump 70 is operated so that lubricant oil is supplied to the first oilgrooves 62, 66 via the first oil-supply channels 72, 74. On the otherhand, when the rotation shaft 15 rotates at a rated rotation speed, thefirst valve 76 is closed, and the pump 70 is stopped so that supply ofthe lubricant oil to the first oil grooves 62, 66 via the firstoil-supply channels 72, 74 is shut off.

According to the second embodiment, adopting a configuration in whichthe first oil-supply channels 72, 74 communicate with each other for theplurality of the first oil grooves 62, 66 disposed along the sameconstant-pressure line makes it possible to simplify the configurationof the oil-supply mechanism 16 such as the first oil-supply channels 72,74 and the valve 73.

Third Embodiment

FIG. 10 is a developed view of a bearing surface of a bearing padaccording to the third embodiment of the present invention.

As illustrated in FIG. 10, in one embodiment, the oil groove 82 mayinclude a pair of rhombus-shaped oil grooves 82 a, 82 b disposed so asto sandwich the oil-supply inlet 80 along the axial direction of therotation shaft 15. In this case, the oil groove 82 may be disposed overthe straight line G₂ passing through the pivot 38, and the vertex parts83 a, 83 b at the upstream side in the rotational direction in thecircumferential direction of the rhombus shape of the oil groove 80 maybe disposed at the upstream side in the rotational direction as comparedto the straight line G₂. In the embodiment illustrated in FIG. 10, theoil groove 82 has a shape symmetric with respect to the straight lineG₂.

Fourth Embodiment

FIG. 11 is a cross-sectional view of a bearing pad according to thefourth embodiment of the present invention. FIG. 12 is a developed viewof a bearing surface according to the fourth embodiment of the presentinvention. FIG. 13 is a diagram for describing a weighted mean positionof an oil groove. Here, FIG. 12 is a planar developed view of a bearingpad 14 having a curvature.

In FIG. 11, G₁ is a straight line passing through the center of therotation shaft 15 and the support point of the pivot 38. In FIG. 12, Cis a straight line passing through the middle position of the bearingpad (bearing surface 14 a) in the rotational direction of the rotationshaft 15. The middle position C is parallel to the axis of the rotationshaft 15. G₂ is a straight line passing through the support point of thebearing pad 14 supported by the pivot 38, extending in parallel to theaxis of the rotation shaft 15. The arrow “a” represents the axialdirection of the rotation shaft 15. Further, in FIGS. 12 and 13, therotational direction of the rotation shaft 15 is represented by x-axis,and the position of the straight line G₂ passing through the supportpoint (the arranged position of the support member) of the pivot 38 isset to be x_(G)=0. Further, the downstream side of the straight line G₂passing through the support point of the pivot 38 in the rotationaldirection (the right side in FIGS. 12 and 13) is referred to aspositive, and the upstream side of the straight line G₂ in therotational direction (the left side in FIGS. 12 and 13) is referred toas negative.

Each bearing pad 14 is supported so as to be pivotable by the pivot 38disposed on the inner circumferential surface of the housing segment 12b. In some embodiments, the pivot 38 is disposed offset toward theupstream side or the downstream side in the rotational direction of therotation shaft 15, from the middle position C of the bearing pad 14 inthe rotational direction of the rotation shaft 15. In the embodimentillustrated in FIG. 12, the arrangement position of the pivot 38 (thesupport point of the bearing pad 14) is disposed offset toward thepositive direction (the downstream side in the rotational direction) ofx-axis with respect to the middle position C of the bearing pad 14. Forinstance, as illustrated in FIG. 1, given that the leading edge 14 b inthe rotational direction is 0% and the trailing edge 14 c in therotational direction is 100%, the pivot 38 is disposed at a position of60%, for instance.

An oil-supply inlet 80 is disposed, and an oil groove 82 communicatingwith the oil-supply inlet 80 is engraved, on the bearing surface 14 a ofthe bearing pad 14. The oil groove 82 includes a pair of rhombus-shapedoil grooves disposed on either side of the rotation shaft 15 of theoil-supply inlet 80, in the axial direction. The oil groove 82 isdisposed so that the weighted mean position X_(A) of the oil groove 82is offset from the straight line G₂ passing through the arrangementposition of the pivot 38, in an offset direction of the support point ofthe pivot 38 with reference to the middle position C of the bearing pad14, which is a direction toward the downstream side in the rotationaldirection in the embodiment exemplarily illustrated in FIGS. 11 and 12.Here, the weighted mean position of the oil groove 82 is a valuerepresenting the mean of the middle position C of the oil groove 82 inthe circumferential direction of the rotation shaft 15 weighted by anopening area of the oil groove 82, which will be described below indetail.

With reference to FIG. 13, the configuration of the oil groove will bedescribed in detail. In FIG. 13, as an example, two oil grooves 90 a and90 b having different opening areas are disposed on either side of thestraight line G₂ passing through the support point of the pivot 38. Theoil groove 90 a is disposed on the downstream side of the straight lineG₂ in the rotational direction of the rotation shaft 15 (the right sideof the straight line G₂ in FIG. 13), while the oil groove 90 b isdisposed on the upstream side of the straight line G₂ in the rotationaldirection (the left side of the straight line G₂ in FIG. 13). Herein,the position of the straight line G₂ on the x-axis is regarded as theorigin (X_(G)=0). Thus, the coordinate X₁ representing the centerposition of the oil groove 90 a on the x-axis is positive (X₁>0), andthe coordinate X₂ representing the center position of the oil groove 90b on the x-axis is negative (X₂<0).

In the present embodiment, the oil groove 90 a and the oil groove 90 bare configured such that the weighted mean position X_(A) of the oilgrooves 90 a, 90 b is offset from the straight line G₂ passing throughthe support point of the pivot 38 (the arrangement position of the pivot38) in the offset direction of the support point of the pivot 38 withreference to the middle position C of the bearing pad 14. In the exampleillustrated in FIG. 13, the pivot 38 is disposed offset toward thedownstream side, in the rotational direction, of the middle position Cin the rotational direction of the rotation shaft 15, where the offsetdirection is along the rotational direction. In this case, the oilgroove 90 a and the oil groove 90 b are each formed so that the weightedmean position A of the oil groove 90 a and the oil groove 90 b is offsettoward the downstream side of the straight line G₂ passing through thesupport point of the pivot 38 in the rotational direction (so that arelationship x_(A)>x_(G) is satisfied).

Although not illustrated, in another embodiment, the pivot 38 isdisposed offset toward the upstream side, in the rotational direction,of the middle position C in the rotational direction of the rotationshaft 15. In this case, the oil groove 90 a and the oil groove 90 b areeach formed so that the weighted mean position of the oil groove 90 aand the oil groove 90 b is offset toward the upstream side of thestraight line G₂ passing through the support point of the pivot 38 inthe rotational direction.

A moment about the support point of the bearing pad 14 supported by thepivot 38 is applied to the bearing pad 14 of the tilting-pad bearingdevice 10, in accordance with the distribution of the oil-film pressure(see FIG. 11) formed between the rotation shaft 15 and the bearing pad14 during operation of the JOP mechanism (i.e., while the lubricant oilis supplied) at the beginning of rotation of the rotation shaft 15 or atlow-speed rotation of the rotation shaft 15. This moment is obtained byadding up local moments of all positions on the bearing surface 14 a,each local moment being a product of the oil-film pressure at a certainposition on the bearing surface 14 a and a distance between the certainposition and the support point. The local moments have opposite signs ateither side of the support point of the bearing pad 14 supported by thepivot 38. Thus, the direction of the net moment corresponding to thedistribution of the oil-film pressure formed between the rotation shaft15 and the bearing pad 14 is determined depending on the magnituderelationship of the absolute value of the moment at either side of thesupport point of the bearing pad 14 supported by the pivot 38. Here, thecontribution of each oil groove 90 a, 90 b to the local moment isrepresented by a product x_(i)S_(i) of the center position x_(i) (i=1,2) of each oil groove 90 a, 90 b and the opening area S_(i) (i=1, 2) ofeach oil groove 90 a, 90 b affecting the magnitude of the oil-filmpressure formed by each oil groove 90 a, 90 b. Thus, the direction ofthe net moment corresponding to the distribution of the oil-filmpressure is basically determined by the sum Σx_(i)S_(i) (i=1, 2) ofcontribution to the local moment in each oil groove 90 a, 90 b. In otherwords, the direction of the net moment corresponding to the distributionof the oil-film pressure is determined depending on the arrangementrelationship between the position of the pivot 38 and a value obtainedby dividing the sum Σx_(i)S_(i) by the sum ΣS_(i) of the opening areasof all oil grooves. The value here is the weighted mean position x_(A)of the oil grooves representing a mean position of the center positionsx_(i) of the respective oil grooves weighted by the opening areas S_(i)of the oil grooves 90 a, 90 b.

In the above tilting-pad bearing device 10, the weighted mean positionX_(A) of the oil grooves 90 a, 90 b representing the mean position ofthe center positions x_(i) of the respective oil grooves 90 a, 90 bweighted by the opening areas S_(i) of the oil grooves is offset in anoffset direction of the pivot 38 from the arrangement position of thepivot 38. Thus, even if the pivot 38 is offset from the middle positionx_(c) of the bearing pad 14, it is possible to balance the momentapplied to the upstream side and the downstream side of the rotationshaft 15 in the rotational direction with reference to the pivot 38. Inthis way, it is possible to restrict inclination of the rotation shaft15, and to prevent the rotation shaft 15 from contacting the bearing pad14, at the beginning of rotation of the rotation shaft 15 or atlow-speed rotation of the rotation shaft 15. Thus, it is possible torotate the rotation shaft 15 smoothly. While two oil grooves 90 a, 90 bare disposed on the bearing surface 14 a in the example illustrated inFIG. 13, the number, shape, arrangement configuration and the like ofthe oil grooves are not limited.

According to the above embodiment, it is possible to balance the momentapplied to the upstream side and the downstream side of the rotationshaft in the rotational direction with reference to the pivot 38, withthe weighted mean position of the oil grooves being offset from thearrangement direction of the pivot 38 in the offset direction based onthe middle position of the pivot 38. In this way, it is possible torestrict inclination of the rotation shaft, and to prevent the rotationshaft from contacting the bearing pad at the beginning of rotation ofthe rotation shaft or at low-speed rotation of the rotation shaft. Thus,it is possible to rotate the rotation shaft smoothly.

In one embodiment, a gap s1 may be formed between the outercircumferential surface of the rotation shaft 15 and the leading edge 14b of the bearing pad 14 in the rotational direction, and a gap s2 may beformed between the outer circumferential surface of the rotation shaft15 and the trailing edge 14 c of the bearing pad 14 in the rotationaldirection, so that the total moment about the pivot in the hydraulicdistribution P due to JOP formed on the bearing surface 14 a is balancedbetween the upstream side and the downstream side of the pivot 38 in therotational direction (direction “r” in the drawing) across the positionof the pivot 38.

The positions of the oil-supply inlet 80 and the oil groove 82 may bedisposed in a region at the further downstream side of the pivot 38 inthe rotational direction, where the gap s1 becomes equivalent to the gaps2 when the total moment about the pivot in the hydraulic distribution Pdue to JOP is balanced between the upstream region and the downstreamregion of the pivot 38 in the rotational direction. The oil-supply inlet80 is disposed at the 70% position, for instance.

As described above, with the oil-supply inlet 80 and the oil groove 82disposed in a downstream region of the pivot 38 in the rotationaldirection, it is possible to secure a thickness of the oil film in thedownstream region in the rotational direction. Further, with theoil-supply inlet 80 and the oil groove 82 disposed in a region where thegap s1 is equivalent to the gap s2, it is also possible to secure athickness of the oil film in the upstream region in the rotationaldirection. In this way, it is also possible to maintain a uniformoil-film pressure over the entire region on the bearing surface 14 a.

Fifth Embodiment

Next, the fifth embodiment of the present invention will be describedwith reference to FIGS. 14 and 15. FIG. 14 is a developed view of abearing surface of a bearing pad according to the fifth embodiment ofthe present invention. FIG. 15 is a diagram of pressure distribution ofan oil film according to the fifth embodiment of the present invention.

As illustrated in FIG. 14, in the present embodiment, a plurality ofoil-supply inlets 140 a and 140 b is disposed on the bearing pad 14. Theoil-supply inlets 140 a and 140 b respectively communicate with the oilgrooves 142 a and 142 b. The oil-supply inlet 140 a is connected to apump 50 which supplies high-pressure lubricant oil to the oil-supplyinlets 140 a and 140 b via oil-supply channels 144 a and 146 a formedthrough the bearing pad 14. The oil-supply inlet 140 b is connected tothe pump 50 via oil-supply channels 144 b and 146 b formed through thebearing pad 14. A valve (flow-rate adjustment valves 148 and 148 b) isdisposed in each of the oil-supply channel 146 a and 146 b. The oilgrooves 142 a and 142 b have a rhombus shape and formed independentlyfrom each other at positions separated in the axial direction (directionof arrow “a”).

Here, the oil grooves 142 a, 142 b may be disposed so as to cross overthe straight line G₂ in FIG. 14, and the vertex positions 142 c of therhombus shape of the oil grooves 142 a, 142 b at the upstream side inthe circumferential rotational direction may be disposed at the upstreamside of the straight line G₂ in the rotational direction (the left sidein FIG. 14).

Further, the positional relationship between the pivot and the oilgrooves 142 a, 142 b may be similar to the above fourth embodiment.Specifically, in one embodiment, the arrangement position G₂ of thepivot is offset from the middle position C of the bearing pad 14 withrespect to the rotational direction x of the rotation shaft 15. The twooil grooves 142 a, 142 b are each disposed so that the weighted meanposition X_(A) of the two oil grooves 142 a, 142 b is offset in theoffset direction from the arrangement position C of the pivot. In theexample of FIG. 14, the offset direction is a direction toward thedownstream side of the rotation shaft 15 in the rotational direction(the right side in FIG. 5).

The oil-supply mechanism is configured to supply lubricant oil to theoil-supply inlets 140 a, 140 b via the oil-supply channels 146 a, 146 band the oil-supply channels 144 a, 144 b from the pump 50. At this time,it is possible to adjust the pressures of lubricant oil “o” flowingthrough the oil-supply channels 146 a, 146 b individually with therespective valves 148 a, 148 b. According to the present embodiment, inaddition to the advantageous effect achieved by the fourth embodiment,if there is partial contact in the axial direction of the rotation shaft15, it is possible to eliminate the partial contact by increasing theamount of lubricant oil supplied to the oil groove in a region with thepartial contact and increasing the oil-film pressure.

Sixth Embodiment

Next, the sixth embodiment of the present invention will be describedwith reference to FIGS. 16 and 17. FIG. 16 is a developed view of abearing surface of a bearing pad according to the sixth embodiment ofthe present invention. FIG. 17A is a diagram of pressure distribution ofan oil film in the oil groove according to the fourth embodiment, andFIG. 17B is a diagram of pressure distribution of an oil film in the oilgroove according to the sixth embodiment.

When the rotation shaft 15 is rotating at a high speed, supply of thelubricant oil to the oil-supply inlet disposed on the bearing surface 14a of the bearing pad 14 is stopped. At this time, the lubricant oilforms an oil-film pressure while rotating along with the rotation shaft15, so as to form the distribution of the oil-film pressure illustratedin FIG. 16. The distribution of the oil-film pressure illustrated inFIG. 16 is similar to that described with reference to FIG. 3.Specifically, in FIG. 16, the lines p1 to p5 are constant-pressure linesof a wedge-shaped oil film formed from rotation of the shaft, where theinner region of p1 represents the maximum oil-film pressure, and theoil-film pressure decreases in sequence toward the outer side. Asillustrated in the drawing, the distribution has an ellipse shape inwhich the constant pressure regions expand in a concentric fashion fromthe maximum oil-film pressure region R₁ at the center. Here, aconstant-pressure line is a line connecting the positions having thesame pressure of the oil film formed between the bearing surface 14 aand the outer circumferential surface of the rotation shaft 15 when therotation shaft 15 rotates.

In the present embodiment, each of the oil-supply inlets 152 a and 152 bis disposed on the constant-pressure line p4. Further, the oil groove154 a communicating with the oil-supply inlet 152 a is disposed alongthe constant-pressure line p4, and similarly, the oil groove 154 bcommunicating with the oil-supply inlet 152 b is disposed along theconstant-pressure line p4. The oil groove 154 a and the oil groove 154 bare independent from each other.

Each oil groove 154 a, 154 b is formed by a single communicating space.Thus, the pressure is the same at any position in each of the oilgrooves 154 a, 154 b. Accordingly, if the oil grooves 42, 44 were formedso as to cross a constant-pressure line, the pressures in the respectiveoil grooves 154 a, 154 b could be averaged upon rotation of the rotationshaft 15, hindering the function as a hydrodynamic bearing.

In view of this, as in the above embodiment, each oil groove 154 a, 154b is disposed along a constant pressure line, which makes it possible tomaintain the pressures inside the oil grooves 154 a, 154 b at therespective constant-pressure line positions, and to maintain a goodfunction as a hydrodynamic bearing.

Since the oil-film pressure is maintained to be constant in the entireregion of each of the oil groove 154 a or the oil groove 154 b, theoil-film pressure does not decrease in the oil groove 154 a or 154 b.

This phenomenon will be described with reference to FIG. 17. FIG. 17A isa diagram illustrating the oil groove 82 of the fourth embodiment, andFIG. 17B is a diagram illustrating the oil groove 154 a of the presentembodiment. There is a risk that the rhombus-shaped oil groove 82 isdisposed so as to cross constant-pressure lines having differentoil-film pressures. Thus, as illustrated in FIG. 17A, the entire regionof the oil groove 82 may have the oil-film pressure of the low pressureside, which may generate a low-pressure region Pr in the oil-filmpressure distribution pa having a wedge shape due to rotation of theshaft. In contrast, the oil-film pressure is constant in the entireregion of the oil groove 154 a or 154 b of the present embodiment. Thus,as illustrated in FIG. 17B, no low-pressure region is generated in theoil-film pressure distribution pb having a wedge shape due to rotationof the shaft.

Further, the oil groove 154 a and 154 b are arranged symmetrically inthe axial direction with respect to the pivot 38. Thus, it is easy toform the same oil-film pressure in the axial direction of the rotationshaft 15. Thus, it is possible to restrict partial contact of therotation shaft 15.

Here, the oil grooves 154 a or 154 b may be disposed so as to cross overthe straight line G₂ in FIG. 16, and the oil-groove end portion 154 c ofthe oil groove 154 a or 154 b at the upstream side in the rotationaldirection may be positioned at the upstream side of the straight line G₂in the rotational direction.

Further, with the configuration of the oil-supply mechanism describedwith reference to the fifth embodiment, it is possible to preventpartial contact of the rotation shaft 15 by adjusting the supplypressure of the lubricant oil to the oil-supply inlets 152 a, 152 bindependently.

Further, as described in the fourth and fifth embodiments, the weightedmean position x_(A) of the oil grooves 154 a and 154 b with respect tothe rotational direction of the rotation shaft 15 may be disposed so asto be offset from the straight line G₂ passing through the arrangementposition of the pivot in the offset direction of the pivot withreference to the middle position of the bearing pad 14, which is adirection toward the downstream side in the rotational direction in theembodiment illustrated in FIG. 16.

Further, the position of the oil grooves 154 a and 154 b with respect tothe rotational direction of the rotation shaft 15 may be in a regionsuch that the gap s1 and the gap s2 (see FIG. 11) become equivalent whenthe total moment about the pivot in the oil-film pressure distribution Pdue to JOP is balanced between the upstream region and the downstreamregion of the pivot in the rotational direction.

Next, a modified example of the above sixth embodiment will be describedwith reference to FIGS. 18 and 19. FIG. 18 is a developed view of abearing surface of a bearing pad according to a modified example of thesixth embodiment. FIG. 19 is a cross-sectional view of a bearing devicefor illustrating an oil-supply mechanism according to a modified exampleof the sixth embodiment.

The oil-supply mechanism illustrated in FIGS. 18 and 19 include thefirst oil-supply inlets 156 c, 156 d, the first oil grooves 158 c, 158d, the second oil-supply inlets 157 a, 157 b, the second oil grooves 159a, 159 b, the first oil-supply channel 146 f, the second oil-supplychannel 146 e, the first valve 148 e, the second valve 148 d, and thepump 50.

The first oil grooves 158 c, 158 d and the second oil grooves 159 a, 159b are disposed along constant-pressure lines representing differentoil-film pressures. The first oil channel 146 f and the second oilchannel 146 e are provided as separate systems so as to be capable ofmaintaining pressures different from one another, at least when therotation shaft 15 is rotating. The first oil channel 146 f and thesecond oil channel 146 e are connected to the pump 50, so that thelubricant oil is supplied by the pump 50. The first valve 148 e isdisposed between the first oil channel 146 f and the pump 50, while thesecond valve 148 d is disposed between the second oil channel 146 e andthe pump 50, so as to be capable of adjusting the amount of lubricantoil supplied to the first oil channel 146 f and the second oil channel146 e, respectively.

At the beginning of rotation of the rotation shaft 15 or at low-speedrotation of the rotation shaft 15, the first valve 148 e and the secondvalve 148 d are opened and the pump 50 is operated, so as to supply thelubricant oil to the first oil groove 158 c (158 d) and the second oilgroove 159 a (159 b) via the first oil channel 146 f and the second oilchannel 146 e. The amount of lubricant oil supplied to each oil groove158 c, 159 a may be adjusted by the opening degree of each valve 148 e,148 d. On the other hand, when the rotation shaft 15 rotates at a ratedrotation speed, the first valve 148 e and the second valve 148 d areclosed and the pump 50 is stopped so as to shut off supply of thelubricant oil to the first oil groove 158 c (158 d) and the second oilgroove 159 a (159 d) via the first oil channel 146 f and the second oilchannel 146 e. At this time, the first oil groove 158 c (158 d) and thesecond oil groove 159 a (159 b) are not in communication with eachother, and thus the pressures in the respective oil grooves 158 c (158d), 159 a (159 b) are independently maintained.

As described above, with the first oil-supply channel 146 ecommunicating with the first oil groove 157 a and the second oil-supplychannel 146 f communicating with the second oil groove 146 c provided asseparate systems so as to be capable of maintain pressures differentfrom each other at least when the rotation shaft 15 is rotating, is itpossible to avoid the pressures in the first oil groove 157 a and thesecond oil groove 156 c disposed along different constant-pressure lines(the first and second constant-pressure lines) from being averaged whenthe rotation shaft 15 rotates at a rated rotation speed, which makes itpossible to maintain a good function as a hydrodynamic bearing.

As described above, an object of the tilting-pad bearing device 10according to at least some embodiments of the present invention is toenable the rotation shaft 15 to levitate with a low supply hydraulicpressure. The tilting-pad bearing device 10 includes a plurality ofbearing pads 14 disposed around a rotation shaft 15 so as to support therotation shaft 15 rotatably, a support member (pivot 38) interposedbetween the plurality of bearing pads 14 and a bearing housing 12supporting the plurality of bearing pads 14, the support membersupporting each of the plurality of bearing pads 14 pivotably, and anoil-supply mechanism configured to supply a lubricant oil to at leastone oil groove (42, 46, 62, 66, 82) formed on a bearing surface 14 a ofat least one of the plurality of bearing pads 14. The at least one oilgroove (42, 46, 62, 66, 82) is disposed inside and outside a contactarea S of the bearing surface 14 a which is in contact with an outercircumferential surface of the rotation shaft 15 when the rotation shaft15 is stopped.

Further, an object of the tilting-pad bearing device 10 according to atleast some other embodiments of the present invention is to preventcontact between the rotation shaft 15 and the bearing pad 14. Thetilting-pad bearing device 10 includes a plurality of bearing pads 14disposed around a rotation shaft 15 so as to support the rotation shaft15 rotatably, a support member (pivot 38) interposed between theplurality of bearing pads 14 and a bearing housing 12 supporting theplurality of bearing pads 14, the support member supporting each of theplurality of bearing pads 14 pivotably, and an oil-supply mechanismconfigured to supply a lubricant oil to at least one oil groove 82formed on a bearing surface 14 a of at least one of the plurality ofbearing pads 14.

The support member (pivot 38) is disposed so as to be offset from amiddle position C of the at least one bearing pad 14 in a rotationaldirection of the rotation shaft 15, toward an upstream side or adownstream side in the rotational direction of the rotation shaft 15.

A weighted mean position x_(A) of the at least one oil grooverepresenting a mean position of a respective center position x_(i) ofthe at least one oil groove 82 in a circumferential direction of therotation shaft 15 weighted by a respective opening area of the at leastone oil groove 82 is offset from an arrangement position G₂ of thesupport member (pivot 38), in an offset direction of the support member(pivot 38) based on the middle position C.

Embodiments of the present invention were described in detail above, butthe present invention is not limited thereto, and various amendments andmodifications may be implemented within a scope that does not departfrom the present invention. For instance, some of the above first tosixth embodiments may be combined upon implementation.

DESCRIPTION OF REFERENCE NUMERAL

-   10 Tilting-pad bearing device-   12 Bearing housing-   12 a, 12 b Housing segment-   14 Bearing pad-   14 a Bearing surface-   15 Rotation shaft-   16 Oil-supply mechanism-   18 Pump-   20 Motor-   22 Oil-supply line-   24 Relief valve-   26 Tank-   28 a, 28 b Branch channel-   30 a, 30 b Valve-   34 Oil-supply inlet-   36 Oil groove-   38 Pivot-   40 (40 a, 40 b) First oil-supply inlet-   42 (42 a, 42 b) First oil groove-   44 (44 a, 44 b) Second oil-supply inlet-   46 (46 a, 46 b) Second oil groove-   50 Pump-   P Distribution of oil-film pressure due to JOP-   Pr Low pressure region-   R₁ Maximum oil-film pressure region-   o Lubricant oil-   pa, pb Pressure distribution of a wedge-shaped oil film formed from    rotation of the shaft-   p1 to p5 Constant-pressure lines of a wedge-shaped oil film formed    from rotation of the shaft-   s1, s2 Gap-   S Contact area

1. A tilting-pad bearing device, comprising: a plurality of bearing padsdisposed around a rotation shaft so as to support the rotation shaftrotatably; a support member interposed between the plurality of bearingpads and a bearing housing supporting the plurality of bearing pads, thesupport member supporting each of the plurality of bearing padspivotably; and an oil-supply mechanism configured to supply a lubricantoil to at least one oil groove formed on a bearing surface of at leastone of the plurality of bearing pads, wherein each of the at least oneoil groove is disposed along a constant pressure line passing throughpositions having same pressure of an oil film formed between the bearingsurface and the outer circumferential surface of the rotation shaft whenthe rotation shaft is rotating.
 2. The tilting-pad bearing deviceaccording to claim 1, wherein the at least one oil groove comprises atleast one first oil groove disposed along a first constant pressure linepassing through positions where the pressure of the oil film is a firstpressure, and at least one second oil groove disposed along a secondconstant pressure line passing through positions where the pressure ofthe oil film is a second pressure which is different from the firstpressure, wherein the oil-supply mechanism includes a first oil-supplychannel communicating with the at least one first oil groove, and asecond oil-supply channel communicating with the at least one second oilgroove, and wherein the first oil-supply channel and the secondoil-supply channel are separate systems capable of maintaining pressuresdifferent from each other at least when the rotation shaft is rotating.3. The tilting-pad bearing device according to claim 2, wherein the atleast one first oil groove disposed along the first constant pressureline comprises a plurality of first oil grooves communicating with eachother via the first oil-supply channel.
 4. The tilting-pad bearingdevice according to claim 2, further comprising: a first valve foradjusting an amount of the lubricant oil supplied to the at least onefirst oil groove, the first valve being disposed in the first oil-supplychannel; and a second valve for adjusting an amount of the lubricant oilsupplied to the at least one second oil groove, the second valve beingdisposed in the second oil-supply channel.
 5. The tilting-pad bearingdevice according to claim 1, wherein the support member is disposed soas to be offset from a middle position of the at least one bearing padin a rotational direction of the rotation shaft, toward an upstream sideor a downstream side in the rotational direction of the rotation shaft,and wherein a weighted mean position of the at least one oil grooverepresenting a mean position of a respective center position of the atleast one oil groove in a circumferential direction of the rotationshaft weighted by a respective opening area of the at least one oilgroove is offset from an arrangement position of the support member, inan offset direction of the support member based on the middle position.6. The tilting-pad bearing device according to claim 5, wherein thesupport member is disposed on the downstream side, in the rotationaldirection of the rotation shaft, of the middle position of the bearingpad in the circumferential direction of the rotation shaft, and whereinthe weighted mean position of the at least one oil groove is offsettoward the downstream side in the rotational direction of the rotationshaft from the arrangement position of the support member.
 7. Thetilting-pad bearing device according to claim 1, wherein a plurality ofoil-supply inlets which is supplied with the lubricant oil from theoil-supply mechanism is disposed on the bearing surface so as to bearranged in a line in an axial direction of the rotation shaft, each ofthe plurality of oil-supply inlets communicating with corresponding oneof the at least one oil groove formed independently from one another. 8.The tilting-pad bearing device according to claim 1, wherein the atleast one oil groove is disposed within a region in which an oil-filmpressure due to a wedge-shaped oil film formed on the bearing surfacewhen the rotation shaft is rotating is uniform.
 9. The tilting-padbearing device according to claim 1, wherein, when the rotation shaft isrotating, a constant-pressure region in which an oil-film pressure dueto a wedge-shaped oil film formed on the bearing surface is uniform isformed such that a maximum oil-film pressure region is at a center and aregion having a gradually decreasing oil-film pressure spreads outwardlyfrom the maximum oil-film pressure region in a concentric fashion, andwherein the at least one oil groove is disposed along one constantpressure line.
 10. The tilting-pad bearing device according to claim 1,wherein a gap between the rotation shaft and an upstream end of thebearing pad in the rotational direction is distributed in a rangeequivalent to a gap between the rotation shaft and a downstream end ofthe bearing pad in the rotational direction, due to an oil-film pressuregenerated between the outer circumferential surface of the rotationshaft and the bearing surface when the rotation shaft is rotating.